1. Field of the Invention
The invention relates to a device for receiving seismic signals and transmitting them to a central control and recording system.
More particularly, the invention relates to a reception and transmission device in which the signals received by a plurality of sensors distributed inside the successive elements of a seismic streamer of great length, are gathered together previous to transmission thereof in electronic acquisition apparatus.
The signals received by each of the acquisition apparatus during the same transmission-reception cycle are sampled, digitized and recorded.
After each cycle and, controlled by the central system, the different acquisition apparatus transmit one after the other and sequentially the data which they have collected over one or more common transmission channels.
2. Description of the Prior Art
The electronic acquisition apparatus are disposed for example in rigid boxes inserted between the elements of the seismic streamer. Such a device is described for example in the U.S. Pat. No. 4,398,271.
The present tendancy in the geophysic field is the lengthening of the seismic streamers.
Increasing the total number of receivers both reduces the intertrace, that is to say the gap between two successive positions of the seismic profile restored (or restituted) by two adjacent recorded traces and also, by combining and processing the recorded signals, increases the sharpness of restoring of the recordings.
The number of inserted electronic apparatus and the density of integration of the components which are contained therein increase.
The fact that the boxes are thus made heavier has numerous drawbacks particularly in marine seismic prospection where the streamers are formed of a plurality of elements filled with a liquid having a density less than that of water, which provides them with a certain buoyancy.
The presence of relatively heavy boxes between the elements makes the distribution of the masses even more unequal, which results in increasing the drag and consequently the parasite flow noises which are superimposed on the useful signals.
The length of the connections between sensors and acquisition apparatus which may reach in some cases several tens of meters, considerably increases their sensitivity to parasite signals. This is particularly true in the case where acoustic receivers other than ceramic sensors are used in the streamers, particularly hydrophones of great length and of continuous structure, whose capacity is lower, for the same sensitivity.
The device of the invention overcomes the above mentioned drawbacks.